U.S. patent application number 14/298563 was filed with the patent office on 2014-11-20 for laser system and laser light generation method.
This patent application is currently assigned to GIGAPHOTON INC.. The applicant listed for this patent is Gigaphoton Inc.. Invention is credited to Takashi Onose, Osamu Wakabayashi, Masaya Yoshino.
Application Number | 20140341239 14/298563 |
Document ID | / |
Family ID | 46927221 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140341239 |
Kind Code |
A1 |
Yoshino; Masaya ; et
al. |
November 20, 2014 |
LASER SYSTEM AND LASER LIGHT GENERATION METHOD
Abstract
A laser system may include: a master oscillator configured to
output pulsed laser light; an amplification device for amplifying
the pulsed laser light from the master oscillator; a first timing
detector configured to detect a first timing at which the master
oscillator outputs the pulsed laser light; a second timing detector
configured to detect a second timing at which the amplification
device discharges; and a controller configured to, based on results
of detection by the first timing detector and the second timing
detector, control at least one of the first timing and the second
timing so that the amplification device discharges when the pulsed
laser light passes through a discharge space of the amplification
device.
Inventors: |
Yoshino; Masaya; (Oyama-shi,
JP) ; Onose; Takashi; (Oyama-shi, JP) ;
Wakabayashi; Osamu; (Hiratsuka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gigaphoton Inc. |
Oyama-shi |
|
JP |
|
|
Assignee: |
GIGAPHOTON INC.
Oyama-shi
JP
|
Family ID: |
46927221 |
Appl. No.: |
14/298563 |
Filed: |
June 6, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13427568 |
Mar 22, 2012 |
|
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14298563 |
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Current U.S.
Class: |
372/25 |
Current CPC
Class: |
H01S 3/134 20130101;
H01S 3/2251 20130101; H01S 3/0057 20130101; H01S 3/2316 20130101;
H01S 3/1636 20130101; H01S 3/2333 20130101; H01S 3/2325 20130101;
H01S 3/0092 20130101; H01S 3/10023 20130101; H01S 3/1305 20130101;
H01S 3/2308 20130101; H01S 3/11 20130101; H01S 3/2366 20130101 |
Class at
Publication: |
372/25 |
International
Class: |
H01S 3/11 20060101
H01S003/11; H01S 3/225 20060101 H01S003/225; H01S 3/13 20060101
H01S003/13; H01S 3/10 20060101 H01S003/10; H01S 3/134 20060101
H01S003/134 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2011 |
JP |
2011-071168 |
Claims
1-12. (canceled)
13. A laser system comprising: a master oscillator including a seed
laser and an amplifier and configured to generate pulsed laser
light; an amplification device configured to amplify the pulsed
laser light from the master oscillator; a first timing detector
configured to detect a first timing at which the pulsed laser light
passes through a predetermined position; a second timing detector
configured to detect a second timing at which the amplification
device discharges; and a controller configured to, based on results
of detection by the first timing detector and the second timing
detector, control at least one of the first timing and the second
timing so that the amplification device discharges when the pulsed
laser light passes through a discharge space of the amplification
device.
14. The laser system according to claim 13, wherein the controller
is configured to calculate a difference between the first timing
and the second timing, and control at least one of a timing at
which the master oscillator outputs pulsed laser light and a timing
at which the amplification device discharges based on the
calculated difference.
15. The laser system according to claim 13, wherein the master
oscillator further includes a pumping laser configured to output
pumping light to the seed laser; wherein the controller is
configured to control at least one of a timing at which the pumping
laser oscillates and a timing at which the amplification device
discharges based on the results of detection by the first timing
detector and the second timing detector.
16. The laser system according to claim 13, wherein the master
oscillator further includes at least one optical shutter disposed
in an optical path between the seed laser and the amplification
device, wherein the predetermined position is a position where the
pulsed laser light passes through after the optical shutter, and
wherein the controller is configured to control at least one of a
timing at which the optical shutter is put into an open state and a
timing at which the amplification device discharges based on the
results of detection by the first timing detector and the second
timing detector.
17. The laser system according to claim 13, wherein the second
timing detector is configured to detect discharge light resulting
from a discharge occurring in the discharge space of the
amplification device as the second timing.
18. The laser system according to claim 13, wherein the
amplification device includes a circuit having a magnetic switch
for causing a discharge in the discharge space, and the second
timing detector is configured to detect turning on and off of the
magnetic switch as the second timing.
19. The laser system according to claim 13, wherein the second
timing detector includes a current sensor and is configured to
detect a timing at which a current caused by discharge produced at
the discharge space of the amplification device flows as the second
timing.
20. The laser system according to claim 16, wherein the seed laser
is configured to output the pulsed laser light having a pulse
duration that is longer than the period for which the controller
puts the optical shutter in the open state.
21. The laser system according to claim 16, wherein the optical
shutter includes: an electro-optical element; a first optical
filter disposed on an optical input end side of the electro-optical
element; a second optical filter disposed on an optical output end
side of the electro-optical element; and a power source connected
to the electro-optical element, the power source being configured
to apply a voltage to the electro-optical element.
22. The laser system according to claim 21, wherein the
electro-optical element is a Pockels cell.
23. The laser system according to claim 21, wherein each of the
first and second optical filters includes at least one
polarizer.
24. A laser system comprising: a master oscillator configured to
generate pulsed laser light; an amplification device configured to
input the pulsed laser light outputted from the master oscillator
and amplify the pulsed laser light; at least one optical shutter
disposed in an optical path of the pulsed laser light to be
inputted into the amplification device; a first timing detector
located on a position below the optical shutter in the optical path
and configured to detect a first timing at which the pulsed laser
light passes therethrough; a second timing detector configured to
detect a second timing at which the amplification device
discharges; and a controller configured to, based on results of
detection by the first timing detector and the second timing
detector, control at least one of a timing at which the master
oscillator outputs pulsed laser light, a timing at which the
optical shutter is put into an open state and a timing at which the
amplification device discharges based on the results of detection
by the first timing detector and the second timing detector.
25. The laser system according to claim 24, wherein the optical
shutter includes: a Pockels cell; a polarizer; a power source
connected to the Pockels cell and configured to apply a voltage to
the Pockels cell.
26. The laser system according to claim 24, wherein the second
timing detector is configured to detect discharge light resulting
from a discharge occurring in the discharge space of the
amplification device as the second timing.
27. The laser system according to claim 24, wherein the
amplification device includes a circuit having a magnetic switch
for causing a discharge in the discharge space, and the second
timing detector is configured to detect turning on and off of the
magnetic switch as the second timing.
28. The laser system according to claim 24, wherein the second
timing detector includes a current sensor and is configured to
detect a timing at which a current caused by discharge produced at
the discharge space of the amplification device flows as the second
timing.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese Patent
Application No. 2011-071168 filed Mar. 28, 2011.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to laser systems and laser
light generation methods.
[0004] 2. Related Art
[0005] Typical ultraviolet light source excimer lasers used in
semiconductor lithography processes include a KrF excimer laser
having a wavelength of approximately 248 nm and an ArF excimer
laser having a wavelength of approximately 193 nm.
[0006] Most such ArF excimer lasers are supplied to market as
two-stage laser systems that include an oscillation stage laser and
an amplifier stage. A basic configuration that is common between
the oscillation stage laser and the amplifier stage in a two-stage
ArF excimer laser system will be described here. The oscillation
stage laser has a first chamber, whereas the amplifier stage has a
second chamber. A laser gas (a mixed gas including F.sub.2, Ar, Ne,
and Xe) is sealed into the respective first and second chambers.
The oscillation stage laser and the amplifier stage also have power
sources that supply electrical energy for pumping the laser gas.
Separate power sources can be supplied for the oscillation stage
laser and the amplifier stage, respectively, but a single power
source can also be shared between the two. First discharge
electrodes including a first anode and a first cathode that are
both connected to the power source are provided within the first
chamber, and likewise, second discharge electrodes including a
second anode and a second cathode that are both connected to the
power source are provided within the second chamber.
[0007] A configuration unique to the oscillation stage laser is,
for example, a line narrowing module. A line narrowing module
typically includes a single grating and at least one prism beam
expander. A semitransparent mirror and the grating configure an
optical resonator, and the first chamber of the oscillation stage
laser is disposed between the semitransparent mirror and the
grating.
[0008] When a charge is generated between the first anode and the
first cathode of the first discharge electrodes, the laser gas is
pumped, and light is generated when the pumping energy is emitted.
This light results in laser light whose wavelength has been
selected by the line narrowing module, and the laser light is
outputted from the oscillation stage laser.
[0009] A two-stage laser system in which the amplifier stage is a
laser including a resonator structure is called "MOPO," whereas a
two-stage laser system in which the amplifier stage does not
include a resonator structure and is not a laser is called "MOPA."
When the laser light from the oscillation stage laser is present
within the second chamber of the amplifier stage, control is
carried out so that a discharge is created between the second anode
and the second cathode of the second discharge electrodes. Through
this, the laser gas within the second chamber is pumped, and the
laser light is amplified and outputted from the amplifier
stage.
SUMMARY
[0010] A laser system according to an aspect of the present
disclosure may include: a master oscillator configured to output
pulsed laser light; an amplification device for amplifying the
pulsed laser light from the master oscillator; a first timing
detector configured to detect a first timing at which the master
oscillator outputs the pulsed laser light; a second timing detector
configured to detect a second timing at which the amplification
device discharges; and a controller configured to, based on results
of detection by the first timing detector and the second timing
detector, control at least one of the first timing and the second
timing so that the amplification device discharges when the pulsed
laser light passes through a discharge space of the amplification
device.
[0011] A laser light generation method according to another aspect
of the present disclosure is a laser light generation method for an
apparatus including a master oscillator, an amplification device, a
first timing detector configured to detect a first timing at which
the master oscillator outputs pulsed laser light, and a second
timing detector configured to detect a second timing at which the
amplification device discharges, and the method may include
controlling, based on results of detection by the first timing
detector and the second timing detector, at least one of the first
timing and the second timing so that the amplification device
discharges when the pulsed laser light passes through a discharge
space of the amplification device.
BRIEF DESCRIPTION OF DRAWINGS
[0012] Embodiments of the present disclosure will be described as
examples hereinafter with reference to the appended drawings.
[0013] FIG. 1 illustrates the general configuration of an example
of a two-stage laser apparatus using a solid-state laser device
having a wavelength conversion element according to a first
embodiment of the present disclosure.
[0014] FIG. 2 illustrates the general configuration of a laser
system according to a second embodiment of the present
disclosure.
[0015] FIG. 3 illustrates an example of an oscillation timing
detection position according to the second embodiment.
[0016] FIG. 4 illustrates an example of a configuration that
measures the timing at which electrical power for a discharge is
supplied according to the second embodiment.
[0017] FIG. 5 illustrates a specific example of a sensor.
[0018] FIG. 6 illustrates another specific example of a sensor.
[0019] FIG. 7 illustrates a case for detecting the actual
occurrence of a discharge in a discharge space using an optical
sensor according to the second embodiment.
[0020] FIG. 8 is a flowchart illustrating an overview of the
operations performed by the laser system according to the second
embodiment of the present disclosure.
[0021] FIG. 9 is a flowchart illustrating an overview of the
operations in a parameter initializing routine, indicated in step
S101 of FIG. 8, according to the second embodiment.
[0022] FIG. 10 is a flowchart illustrating the operations started
by a controller in step S103 of FIG. 8, according to the second
embodiment.
[0023] FIG. 11 is a flowchart illustrating the operations started
by a laser controller in step S104 of FIG. 8, according to the
second embodiment.
[0024] FIG. 12 is a flowchart illustrating details of step S108 of
FIG. 8 according to the second embodiment.
[0025] FIG. 13 illustrates the general configuration of a laser
system according to a third embodiment of the present
disclosure.
[0026] FIG. 14 illustrates an example of an optical shutter
according to the third embodiment.
[0027] FIG. 15 illustrates an example of a high-voltage pulse
applied to a Pockels cell according to the third embodiment.
[0028] FIG. 16 illustrates an example of pulsed laser light
outputted from a long-pulse master oscillator according to the
third embodiment.
[0029] FIG. 17 illustrates an example of the pulsed laser light
that has passed through the optical shutter according to the third
embodiment.
[0030] FIG. 18 is a flowchart illustrating an overview of the
operations in a parameter initializing routine, indicated in step
S101 of FIG. 8, according to the third embodiment.
[0031] FIG. 19 is a flowchart illustrating the operations started
by a controller in step S103 of FIG. 8, according to the third
embodiment.
[0032] FIG. 20 is a flowchart illustrating the operations started
by a laser controller in step S104 of FIG. 8, according to the
third embodiment.
[0033] FIG. 21 is a flowchart illustrating details of step S108 of
FIG. 8 according to the third embodiment.
[0034] FIG. 22 illustrates an example of a Ti:sapphire laser
according to the first through third embodiments.
[0035] FIG. 23 illustrates an example of an amplifier according to
the first through third embodiments.
[0036] FIG. 24 illustrates the general configuration of a
Fabry-Perot amplifier according to the first through third
embodiments.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] Embodiments of the present disclosure will be described in
detail hereinafter with reference to the drawings. The embodiments
described hereinafter indicate examples of the present disclosure,
and are not intended to limit the content of the present
disclosure. Furthermore, not all of the configurations and
operations described in the embodiments are required configurations
and operations in the present disclosure. Note that identical
constituent elements will be given identical reference characters,
and duplicate descriptions thereof will be omitted. The description
is given following the table of contents below.
TABLE OF CONTENTS
[0038] 1. Outline
[0039] 2. Explanation of Terms
[0040] 3. Laser System Including Master Oscillator and
Amplification Device
First Embodiment
[0041] 3.1 Configuration
[0042] 3.2 Operations
[0043] 4. Laser System Performing Feedback Control on
Synchronization of Master Oscillator and Amplification Device
(Second Embodiment)
[0044] 4.1 Configuration
[0045] 4.2 Operations
[0046] 4.3 Effects
[0047] 4.4 Example of Sensor Arrangement for Measuring Oscillation
Timing
[0048] 4.5 Example of Sensor for Measuring Discharge Timing
[0049] 4.5.1 Example of Measuring Discharge Timing Using Sensor
within Laser Power Source
[0050] 4.5.1.1 First Configuration Example of Sensor
[0051] 4.5.1.2 Second Configuration Example of Sensor
[0052] 4.5.2 Example of Measuring Discharge Timing Using Optical
Sensor
[0053] 4.6 Flowcharts
[0054] 5. Laser System Performing Feedback Control on
Synchronization of Master Oscillator Including Optical Shutter and
Amplification Device
Third Embodiment
[0055] 5.1 Configuration
[0056] 5.1.1 Optical Shutter
[0057] 5.2 Operations
[0058] 5.3 Effects
[0059] 5.4 Flowchart
[0060] 6. Additional Descriptions
[0061] 6.1 Ti: Sapphire Laser
[0062] 6.2 Amplifier (PA)
[0063] 6.3 Amplifier Including Optical Resonator (PO)
1. Outline
[0064] In the embodiments described as examples hereinafter, pulsed
laser light outputted from a master oscillator and the operation
(discharge) timing of an amplification device containing a laser
gas may be synchronized.
2. Explanation of Terms
[0065] A "KBBF crystal" is a nonlinear optical crystal expressed by
the chemical formula KBe.sub.2BO.sub.3F.sub.2, and serves as a
wavelength conversion element. "Burst oscillation" refers to
outputting pulsed laser light at a predetermined repetition rate
during a predetermined interval. An "optical path" is a path along
which laser light is transmitted.
3. Laser System Including Master Oscillator and Amplification
Device
First Embodiment
3.1 Configuration
[0066] FIG. 1 illustrates the general configuration of an example
of a two-stage laser apparatus according to a first embodiment of
the present disclosure.
[0067] A two-stage laser apparatus (called a "laser system"
hereinafter) 1 may include a master oscillator 2 and an
amplification device 3. The master oscillator 2 may, for example,
include a wavelength conversion element. The amplification device 3
may, for example, be a discharge-pumped ArF excimer amplifier. A
low-coherence optical system 4 may be disposed between the master
oscillator 2 and the amplification device 3. A system, such as an
optical pulse stretcher, a random phase plate, or the like, may be
employed as the low-coherence optical system 4.
[0068] The master oscillator 2 will be described next. The master
oscillator 2 may include a pumping laser 5, a Ti:sapphire laser 6,
an amplifier 7, a beam splitter 81, a high-reflection mirror 82, an
LBO crystal 9, a KBBF crystal 10, and a high-reflection mirror
11.
[0069] The pumping laser 5 may be a laser that, for example,
oscillates second harmonic light of a semiconductor laser-pumped
Nd:YAG laser. The Ti:sapphire laser 6 may include a Ti:sapphire
crystal and an optical resonator. The amplifier 7 may be an
amplifier that includes a Ti:sapphire crystal.
[0070] The amplification device 3 will be described next. The
amplification device 3 may include a chamber 20, a pair of
discharge electrodes (an anode 21 and a cathode 22), an output
coupling mirror 14, and high-reflection mirrors 15, 16, and 17. A
laser gas may be sealed into the chamber 20. This laser gas may be
a mixed gas of Ar, Ne, F.sub.2, and Xe. The anode 21 and the
cathode 22 may be disposed within the chamber 20. The anode 21 and
the cathode 22 may be disposed with a space provided therebetween
in the direction that follows the depiction in FIG. 1. The anode 21
and the cathode 22 may be disposed in the vertical direction with
respect to the depiction as illustrated in FIG. 1. The space
between the anode 21 and the cathode 22 may be a discharge space
23. Windows 18 and 19, through which pulsed laser light 32 passes,
may be provided in the chamber 20. In addition, a power source (not
shown) may be disposed outside the chamber 20.
[0071] The output coupling mirror 14 and the high-reflection
mirrors 15, 16, and 17 may configure a ring optical resonator. The
output coupling mirror 14 may be an element that allows a part of
light to pass therethrough while reflecting another part of
light.
3.2 Operations
[0072] The master oscillator 2 may output pulsed laser light 31 at
a wavelength of approximately 193 nm. The low-coherence optical
system 4 may then reduce the coherence of the pulsed laser light
31. The amplification device 3 may amplify the pulsed laser light
32, whose coherence has been reduced, and output that light as
pulsed laser light 33. The pulsed laser light 33 may, for example,
be transmitted to a semiconductor exposure apparatus (not shown)
and used in exposure processes.
[0073] Pumping light 51 at a wavelength of approximately 532 nm may
be outputted from the pumping laser 5. Part of the pumping light 51
may pass through the beam splitter 81. Another part of the pumping
light 51 may be reflected by the beam splitter 81. The pumping
light 51 that has passed through the beam splitter 81 may pump the
Ti: sapphire laser 6. Pulsed laser light at a wavelength of
approximately 773.6 nm may be outputted from the pumped laser 6.
Here, the Ti:sapphire laser 6 may include an optical resonator
provided with a wavelength selection element (not shown). Pulsed
laser light having a spectral linewidth that has been narrowed by
the wavelength selection element may be outputted from the
Ti:sapphire laser 6.
[0074] Of the pumping light 51 outputted from the pumping laser 5,
the pumping light 51 reflected by the beam splitter 81 may further
be reflected by the high-reflection mirror 82. The reflected
pumping light 51 may enter the Ti:sapphire amplifier 7 and may then
pump the Ti:sapphire crystal provided therein. The amplifier 7 may
amplify the pulsed laser light outputted from the Ti:sapphire laser
6 using that pumping energy. As a result, pulsed laser light at a
wavelength of approximately 773.6 nm may be outputted from the
amplifier 7.
[0075] The pulsed laser light outputted from the Ti:sapphire
amplifier 7 may be converted into pulsed laser light at a
wavelength of approximately 386.8 nm (one-half of the
aforementioned 773.6 nm) by passing through the LBO crystal 9,
which serves as a wavelength conversion element. The pulsed laser
light that has experienced the wavelength conversion may further be
converted into pulsed laser light 31 at a wavelength of
approximately 193.4 nm (one-half of the aforementioned 386.8 nm) by
passing through the KBBF crystal 10, which serves as a wavelength
conversion element.
[0076] The travel direction of the pulsed laser light 31 that has
passed through the KBBF crystal 10 may be changed by the
high-reflection mirror 11, and may enter the low-coherence optical
system 4. The coherence of the pulsed laser light 31 maybe reduced
by passing through the low-coherence optical system 4. The pulsed
laser light 32 whose coherence has been reduced may then enter the
amplification device 3.
[0077] The power source electrically connected to the anode 21 and
the cathode 22 within the chamber 20 may apply a potential
difference between the anode 21 and the cathode 22. Through this, a
discharge may occur between the anode 21 and the cathode 22 at the
timing at which the pulsed laser light 32 passes through the
discharge space 23 in the amplification device 3.
[0078] Part of the pulsed laser light 32 emitted by the
low-coherence optical system 4 may pass through the output coupling
mirror 14 and be reflected by the high-reflection mirror 15. This
pulsed laser light 32 may then pass through the window 18 and
advance into the discharge space 23 between the anode 21 and the
cathode 22. The pulsed laser light 32 may be amplified by carrying
out control so that a discharge occurs in the discharge space 23
when the pulsed laser light 32 is present in the discharge space
23. The amplified pulsed laser light 32 may be emitted from the
chamber 20 through the window 19. The emitted pulsed laser light 32
may be highly reflected by the high-reflection mirrors 16 and 17,
and may then once again advance into the discharge space 23 within
the chamber 20 via the window 19. This pulsed laser light 32 may
then be emitted from the chamber 20 through the window 18. The
emitted pulsed laser light 32 may then enter the output coupling
mirror 14. Part of the pulsed laser light 32 may pass through the
output coupling mirror 14 and be outputted from the amplification
device 3 as the pulsed laser light 33. Another part of the pulsed
laser light 32 may be returned into the ring optical resonator as
feedback light by being reflected by the output coupling mirror
14.
[0079] Although the case where the amplification device 3 includes
a ring optical resonator is mentioned as an example in these
descriptions, the disclosure is not limited thereto. For example,
the amplification device 3 may include a Fabry-Perot resonator in
which an optical resonator is provided in an amplifier.
4. Laser System Performing Feedback Control on Synchronization of
Master Oscillator and Amplification Device (Second Embodiment)
[0080] Next, a laser system 1A according to a second embodiment of
the present disclosure will be described in detail with reference
to the drawings.
4.1 Configuration
[0081] FIG. 2 illustrates the general configuration of the laser
system 1A according to the second embodiment. As shown in FIG. 2,
the laser system 1A may include a master oscillator 2A, the
high-reflection mirror 11, the low-coherence optical system 4, an
amplification device 3A, and a laser controller 220A. The laser
controller 220A may control the overall operations of the laser
system 1A.
[0082] The master oscillator 2A may include a solid-state laser
device 200 and a controller 210. The solid-state laser device 200
may include, as in the master oscillator 2 illustrated in FIG. 1,
the pumping laser 5, the Ti:sapphire laser 6 (a seed laser), the
amplifier 7, a wavelength conversion unit 8 that includes the LBO
crystal 9 and the KBBF crystal 10, the beam splitter 81, and the
high-reflection mirror 82.
[0083] The controller 210 may be a synchronization control device
that controls the timing at which the pulsed laser light 31 is
outputted. Such a controller 210 may include an internal trigger
oscillator 211. The internal trigger oscillator 211 may, for
example, oscillate an internal trigger at a predetermined
repetition rate. The controller 210 may transmit this internal
trigger to the pumping laser 5 as a pumping laser oscillation
signal S11.
[0084] In addition, the controller 210 may, for example, receive a
trigger signal S1 at an approximately predetermined repetition rate
from the laser controller 220A or the like, which serves as a
higher-level controller. The controller 210 may transmit the
trigger signal S1 received from the laser controller 220A to the
pumping laser 5 as the pumping laser oscillation signal S11.
Through this, the pumping laser 5 can continuously output the
pumping light 51 at the approximately predetermined repetition
rate.
[0085] The master oscillator 2A may include an oscillation delay
circuit 311. The oscillation delay circuit 311 may delay the
pumping laser oscillation signal S11 outputted from the controller
210 to the pumping laser 5 by an amount equivalent to a
predetermined delay time (an oscillation delay time Ddp) in order
to adjust the timing relative to the amplification device 3A.
[0086] In addition, the master oscillator 2A may include a beam
splitter 420 and an optical sensor 410. The beam splitter 420 may
be disposed in the optical path of pulsed laser light L1 that
travels within the solid-state laser device 200. The optical sensor
410 may detect the pulsed laser light L1 split by the beam splitter
420. The result of the detection of the pulsed laser light L1 by
the optical sensor 410 may be inputted into the laser controller
220A via the controller 210. The laser controller 220A may specify
an oscillation timing Tmo of the pulsed laser light L1 based on the
inputted detection result.
[0087] In addition to the same constituent elements as the
amplification device 3 shown in FIG. 1, the amplification device 3A
may include a laser power source 24 and a switch delay circuit 350.
The laser power source 24 may be electrically connected to the
anode 21 and the cathode 22 in the chamber 20. The switch delay
circuit 350 may delay a switch signal S5 outputted from the laser
controller 220A to a switch 25 in the laser power source 24 by an
amount equivalent to a predetermined delay time (a switch delay
time Dpp).
[0088] In addition, the amplification device 3A may include a
sensor 430 that detects a discharge timing Tpo, which is a timing
at which a discharge has occurred in the discharge space 23, or a
timing at which a discharge is caused to occur in the discharge
space 23.
4.2 Operations
[0089] Next, an overview of operations performed by the laser
system 1A will be given. The laser controller 220A may receive,
from an exposure controller 601 in an exposure apparatus 600, a
request for burst output of the pulsed laser light 33. When the
burst output has been requested, the laser controller 220A may
output a burst request signal S2 to the controller 210 of the
master oscillator 2A. In addition, the laser controller 220A may
output the trigger signal S1 to the controller 210 at an
approximately predetermined repetition rate. The controller 210 may
output the trigger signal S1 or the internal trigger generated by
the internal trigger oscillator 211 to the pumping laser 5 as the
pumping laser oscillation signal S11. The pumping laser oscillation
signal S11 may be inputted into the pumping laser 5 having been
delayed by an amount equivalent to a predetermined delay time (the
oscillation delay time Ddp) relative to the input of the trigger
signal S1 by passing through the oscillation delay circuit 311.
When the pumping laser oscillation signal S11 is inputted, the
pumping laser 5 may output the pumping light 51. Through this, the
pulsed laser light L1 may be generated within the solid-state laser
device 200.
[0090] The pulsed laser light L1 generated within the solid-state
laser device 200 may travel along the optical path within the
solid-state laser device 200. The optical sensor 410 may detect the
timing at which the pulsed laser light L1 passes a predetermined
position in the optical path. The result of this timing detection
may be outputted from the optical sensor 410 to the laser
controller 220A via the controller 210. The laser controller 220A
may specify the oscillation timing Tmo of the pulsed laser light L1
based on the inputted detection result.
[0091] The laser controller 220A may output the switch signal S5 to
the laser power source 24 of the amplification device 3 at an
approximately predetermined repetition rate. The laser controller
220A may output the switch signal S5 continuously, or may output
the switch signal S5 only during a period in which burst output is
being requested by the exposure controller 601. The switch signal
S5 may be inputted into the switch 25 of the laser power source 24
having been delayed by an amount equivalent to a predetermined
delay time relative to the output of the trigger signal S1 (the
switch delay time Dpp) by passing through the switch delay circuit
350. When the switch 25 is turned on by the switch signal S5, the
laser power source 24 may apply a potential difference for
discharge between the anode 21 and the cathode 22. As a result, a
discharge can occur in the discharge space 23 between the anode 21
and the cathode 22.
[0092] It is desirable to match the timing at which the discharge
is caused to occur in the discharge space 23 with the timing at
which the pulsed laser light 32, which has entered the
amplification device 3 from the master oscillator 2A through the
low-coherence optical system 4, passes through the chamber 20
(synchronization). The oscillation delay time Ddp and the switch
delay time Dpp for achieving this synchronization may be found in
advance through experience, experiments, or simulations. In
addition, at least one of the oscillation delay time Ddp and the
switch delay time Dpp may undergo feedback control based on a
difference between the timing of the pulsed laser light L1 and the
timing of the discharge. The timing of the pulsed laser light L1
may, for example, be the oscillation timing Tmo of the pumping
laser 5. The timing at which the pulsed laser light L1 passes the
predetermined position may be used as the oscillation timing Tmo.
In addition, the discharge timing may be the discharge timing Tpo
at which a discharge is caused to occur in the discharge space 23.
The timing at which the electric power used for discharge is
supplied between the anode 21 and the cathode 22 may be used as the
discharge timing Tpo.
4.3 Effects
[0093] In the second embodiment, the laser controller 220A may
detect a difference between the timing of the pulsed laser light L1
(for example, the oscillation timing Tmo) and the timing of the
discharge (for example, the discharge timing Tpo). In accordance
with that difference, the laser controller 220A may carry out
feedback control on the oscillation timing Tmo of the pumping laser
5 and the discharge timing Tpo of the amplification device 3A.
Through this, a discharge can be caused to occur in the discharge
space 23 in correspondence with the timing at which the pulsed
laser light 32 passes through the discharge space 23 within the
amplification device 3A. As a result, the influence of drift in the
oscillation timing Tmo and the discharge timing Tpo can be reduced,
which makes it possible to amplify the pulsed laser light 32 in a
more stable manner.
4.4 Example of Sensor Arrangement for Measuring Oscillation
Timing
[0094] Here, an example of the detection position for the
oscillation timing Tmo will be described using FIG. 3. As indicated
by beam splitters 421, 422, and 424, and optical sensors 411, 412,
and 414 in FIG. 3, the detection position for the oscillation
timing Tmo may be at at least one of the output stages including
the Ti:sapphire laser 6, the amplifier 7, and the wavelength
conversion unit 8. Meanwhile, the detection position for the
oscillation timing Tmo may be between the LBO crystal 9 and the
KBBF crystal 10 within the wavelength conversion unit 8, as
indicated by a beam splitter 423 and an optical sensor 413 in FIG.
3.
4.5 Example of Sensor for Measuring Discharge Timing
[0095] An example of a sensor that detects the discharge timing Tpo
will be described hereinafter.
4.5.1 Example of Measuring Discharge Timing Using Sensor within
Laser Power Source
[0096] First, an example in which the timing at which the discharge
voltage is applied between the anode 21 and the cathode 22 is
detected as the discharge timing Tpo will be described. FIG. 4 is
an example of the configuration that measures the timing at which
the discharge voltage is applied. As with the amplification device
3A shown in FIG. 4, in the case where the timing at which the
discharge voltage is applied is detected as the discharge timing
Tpo, the sensor 430 may be disposed within the laser power source
24.
4.5.1.1 First Configuration Example of Sensor
[0097] The sensor 430 will be described in more detail. FIG. 5
illustrates an example of a case in which a magnetic
switch-operated sensor 431 is used as the sensor 430. As shown in
FIG. 5, the magnetic switch-operated sensor 431 may be provided for
a saturable reactor AL1 in a magnetic pulse compression circuit 26
that applies a voltage used to generate a discharge between the
anode 21 and the cathode 22. The saturable reactor AL1 is what is
known as a magnetic switch. The magnetic switch-operated sensor 431
may detect the point in time of saturation of the saturable reactor
AL1. The magnetic switch-operated sensor 431 may output the
detected point in time of saturation to the laser controller 220A.
The laser controller 220A may specify the inputted point in time of
saturation as the discharge timing Tpo.
4.5.1.2 Second Configuration Example of Sensor
[0098] Another example of the configuration of the sensor 430 will
be described. FIG. 6 illustrates an example of a case where a
current sensor 432 is used as the sensor 430. As shown in FIG. 6,
the current sensor 432 may be connected in series between the
magnetic pulse compression circuit 26 and the anode 21. The current
sensor 432 may measure a current value of a current flowing through
the anode 21. The current sensor 432 may output the detected
current value to the laser controller 220A. The laser controller
220A may specify the timing at which the current flows through the
anode 21 as the discharge timing Tpo, based on the inputted current
value.
4.5.2 Example of Measuring Discharge Timing Using Optical
Sensor
[0099] Next, an example of a case where an optical sensor 433 is
used as the sensor 430 will be described. FIG. 7 illustrates a case
where the actual occurrence of a discharge in the discharge space
23 is detected using the optical sensor 433. With an amplification
device 3B illustrated in FIG. 7, a window 433a that allows
discharge light that has occurred in the discharge space 23 to pass
through may be provided in the chamber 20. The discharge light
emitted from the discharge space 23 via the window 433a may be
captured by a light-receiving surface of the optical sensor 433
through a transfer lens 433b. The optical sensor 433 may detect the
occurrence of a discharge in the discharge space 23 by detecting
the captured discharge light. In addition, the optical sensor 433
may output the detection result to the laser controller 220A. The
laser controller 220A may specify the discharge timing Tpo based on
the inputted detection result.
[0100] In addition, the discharge timing Tpo may be detected by the
optical sensor 433 detecting the pulsed laser light 33 emitted from
the chamber 20. In this case, as indicated by the broken line in
FIG. 7, a beam splitter 433c may be disposed in the optical path of
the pulsed laser light 33. Part of the pulsed laser light 33 split
by the beam splitter 433c may enter the optical sensor 433. The
optical sensor 433 may detect the occurrence of a discharge in the
discharge space 23 by detecting the pulsed laser light 33 that has
entered. In addition, the optical sensor 433 may output the
detection result to the laser controller 220A. The laser controller
220A may specify the discharge timing Tpo based on the inputted
detection result.
4.6 Flowcharts
[0101] Next, operations performed by the laser system 1A
illustrated in FIG. 2 will be described in detail with reference to
the drawings. FIG. 8 is a flowchart illustrating an overview of the
operations of the laser system 1A. FIG. 9, meanwhile, is a
flowchart illustrating an overview of the operations performed in a
parameter initializing routine, indicated in step S101 of FIG. 8.
FIG. 10 is a flowchart illustrating the operations started by the
controller 210 in step S103 of FIG. 8. FIG. 11 is a flowchart
illustrating operations started by the laser controller 220A in
step S104 of FIG. 8. FIG. 12 is a flowchart illustrating step S108
of FIG. 8 in detail. Note that FIG. 8, FIG. 9, FIG. 11, and FIG. 12
indicate the operations performed by the laser controller 220A.
FIG. 10, meanwhile, indicates the operations performed by the
controller 210.
[0102] As shown in FIG. 8, after starting up, the laser controller
220A may execute a parameter initializing routine that initializes
various parameters (step S101). Note that the initial parameters to
be set may be recorded in advance, or may be inputted or requested
from an external device, such as from the exposure controller
601.
[0103] Next, the laser controller 220A may stand by until a burst
request signal, requesting a burst of the pulsed laser light 33, is
received from the exposure controller 601 or the like (step S102;
NO). When the burst request signal has been received (step S102;
YES), the laser controller 220A may execute control causing the
master oscillator 2A to output a burst of the pulsed laser light 31
(step S103). Along with this, the laser controller 220A may execute
control causing the amplification device 3A to perform a discharge
(step S104).
[0104] Next, the laser controller 220A may output the trigger
signal S1 to the controller 210 so as to achieve a predetermined
repetition rate (step S105). The laser controller 220A may then
detect the oscillation timing Tmo from the result of the detection
performed by the optical sensor 410 that has been inputted from the
controller 210 (step S106). In addition, the laser controller 220A
may detect the discharge timing Tpo from the detection result
inputted from the sensor 430 (step S107). Next, the laser
controller 220A may correct the switch delay time Dpp of the switch
delay circuit 350 (or the oscillation delay time Ddp of the
oscillation delay circuit 311) based on a time difference between
the oscillation timing Tmo and the discharge timing Tpo (step
S108).
[0105] Thereafter, the laser controller 220A may determine whether
or not to stop the output of the pulsed laser light 33 (step S109).
In the case where the output is to be stopped (step S109; YES), the
laser controller 220A may end the control of the master oscillator
2A started in step S103 (step S110). In addition, the laser
controller 220A may end the control of the amplification device 3A
started in step S104 (step S111), and thereafter, may end the
present operations. On the other hand, in the case where the output
is not to be stopped (step S109; NO), the laser controller 220A may
return to step S103 and execute the operations that follow
thereafter.
[0106] Next, an overview of the operations in the parameter
initializing routine indicated in step S101 of FIG. 8 will be
described. As shown in FIG. 9, in the parameter initializing
routine, the laser controller 220A may obtain the oscillation delay
time Ddp set in the oscillation delay circuit 311 (step S121). The
obtained oscillation delay time Ddp may be a default value stored
in advance in a memory or the like (not shown), or may be a value
newly calculated by the laser controller 220A. Continuing on, the
laser controller 220A may set the obtained oscillation delay time
Ddp in the oscillation delay circuit 311 via the controller 210
(step S122). Note that when setting the oscillation delay time Ddp
in the oscillation delay circuit 311, the laser controller 220A may
carry out the setting through the controller 210, as shown in FIG.
3. Through this, the timing of the pumping laser oscillation signal
S11 that passes through the oscillation delay circuit 311 may be
delayed by an amount equivalent to the oscillation delay time
Ddp.
[0107] Next, the laser controller 220A may obtain the switch delay
time Dpp set in the switch delay circuit 350 (step S123). The
obtained switch delay time Dpp may be a default value stored in
advance in a memory or the like (not shown), or may be a value
newly calculated by the laser controller 220A. Then, the laser
controller 220A may set the obtained switch delay time Dpp in the
switch delay circuit 350 (step S124). Through this, the timing of
the switch signal S5 that passes through the switch delay circuit
350 may be delayed by an amount equivalent to the switch delay time
Dpp.
[0108] Next, the laser controller 220A may obtain a time to turn
the switch 25 on, or in other words, a time for which to apply a
discharge voltage between the anode 21 and the cathode 22 (that is,
a switch-on time .DELTA.Tpp) (step S125). The obtained switch-on
time .DELTA.Tpp may be a default value stored in advance in a
memory or the like (not shown), or may be a value newly calculated
by the laser controller 220A. Thereafter, the laser controller 220A
may return to the operations indicated in FIG. 8.
[0109] Operations started by the controller 210 in step S103 of
FIG. 8 will now be described. As shown in FIG. 10, under the
control of the laser controller 220A, the controller 210 may stand
by until, for example, the trigger signal S1 is received from the
laser controller 220A (step S131; NO).
[0110] When the trigger signal S1 has been received (step S131;
YES), the controller 210 may transmit the trigger signal S1 to the
pumping laser 5 as the pumping laser oscillation signal S11 (step
S132). The pumping laser oscillation signal S11 may be inputted to
the pumping laser 5 through the oscillation delay circuit 311. Note
that the timing at which the pumping light 51 is outputted from the
pumping laser 5 may be directly related to the timing at which the
pulsed laser light L1 is outputted from the Ti:sapphire laser
6.
[0111] Next, the controller 210 may stand by until the result of
detecting the pulsed laser light L1 is inputted from the optical
sensor 410 (step S133; NO). When the detection result is inputted
from the optical sensor 410 (step S133; YES), the controller 210
may transmit the inputted detection result to the laser controller
220A (step S134). After this, the controller 210 may determine
whether or not an end to the operations has been specified by the
laser controller 220A or the like (step S135). In the case where
the end has been specified (step S135; YES), the controller 210 may
end the present operations. However, in the case where the end has
not been specified (step S135; NO), the controller 210 may return
to step S131.
[0112] Next, operations started by the laser controller 220A in
step S104 of FIG. 8 will be described. As shown in FIG. 11, the
laser controller 220A may stand by until the trigger signal S1 is
outputted to the controller 210 (step S141; NO). When the trigger
signal S1 is outputted (step S141; YES), the laser controller 220A
may start the transmission of the switch signal S5 to the switch 25
(step S142). The switch signal S5 may be inputted to the switch 25
through the switch delay circuit 350. The switch delay time Dpp may
be set in the switch delay circuit 350 so that a discharge occurs
in the discharge space 23 in correspondence with the timing at
which the pulsed laser light 32 passes through the discharge space
23.
[0113] Thereafter, the laser controller 220A may measure the time
that has elapsed after the start of the transmission of the switch
signal S5 using, for example, a timer or the like (not shown). The
laser controller 220A may then stand by until the measured time
becomes greater than or equal to the pre-set switch-on time
.DELTA.Tpp (step S143; NO).
[0114] When the switch-on time .DELTA.Tpp has elapsed (step S143;
YES), the laser controller 220A may end the transmission of the
switch signal S5 (step S144). Through this, the period in which a
discharge occurs in the discharge space 23 may be adjusted.
Thereafter, the laser controller 220A may determine whether or not
to end the operations (step S145). In the case where the operations
are to be ended (step S145; YES), the laser controller 220A may end
the present operations. However, in the case where the operations
are not to be ended (step S145; NO), the laser controller 220A may
return to step S141.
[0115] Next, step S108 of FIG. 8 will be described in detail. As
shown in FIG. 12, the laser controller 220A may specify the
oscillation timing Tmo based on the result of the detection
performed by the optical sensor 410 that has been inputted from the
controller 210 (step S151). In addition, the laser controller 220A
may specify the discharge timing Tpo from the detection result
inputted from the sensor 430 (step S152).
[0116] Next, the laser controller 220A may calculate a delay time D
of the discharge timing Tpo relative to the oscillation timing Tmo
(step S153). Next, the laser controller 220A may calculate an error
App of the delay time D relative to a delay time DO that has been
set as a reference (step S154). The laser controller 220A may then
correct the switch delay time Dpp (or the oscillation delay time
Ddp) using the calculated error .DELTA.pp (step S155). Thereafter,
the laser controller 220A may advance the process to step S109 of
FIG. 8.
5. Laser System Performing Feedback Control on Synchronization of
Master Oscillator Including Optical Shutter and Amplification
Device
Third Embodiment
[0117] Next, a laser system 1B according to a third embodiment will
be described in detail with reference to the drawings.
5.1 Configuration
[0118] FIG. 13 illustrates the general configuration of the laser
system 1B according to the third embodiment. As shown in FIG. 13,
the laser system 1B may have a similar configuration to the laser
system 1A shown in FIG. 2. However, in the laser system 1B, the
master oscillator 2A provided in the laser system 1A is replaced
with a master oscillator 2B.
[0119] The master oscillator 2B may further include an optical
shutter 41 and a shutter delay circuit 341, in addition to the same
constituent elements as those in the master oscillator 2A.
Meanwhile, the pumping laser 5, the Ti:sapphire laser 6, and the
beam splitter 81 in the solid-state laser device 200 may configure
a long-pulse master oscillator 60.
[0120] An optical shutter operation signal S41 that controls the
opening/closing operations of the optical shutter 41 may be
inputted into the optical shutter 41 from the controller 210 via
the shutter delay circuit 341. A shutter delay time Dop may be set
in the shutter delay circuit 341 by the laser controller 220A via
the controller 210. The optical shutter operation signal S41 may be
inputted into the optical shutter 41 having been delayed by an
amount equivalent to the shutter delay time Dop by passing through
the shutter delay circuit 341.
[0121] Other configurations are the same as those of the laser
system 1A shown in FIG. 2.
5.1.1 Optical Shutter
[0122] Here, FIG. 14 illustrates an example of an optical shutter
according to the third embodiment. As shown in FIG. 14, the optical
shutter 41 may include, for example, two polarizers 141 and 143, a
Pockels cell 142, and a high-voltage power source 144. The
polarizer 141 may, for example, allow a Y-direction polarized
component of light that has entered to pass and block an
X-direction polarized component of light that has entered. On the
other hand, the polarizer 143 may, for example, allow an
X-direction polarized component of light that has entered to pass
and block a Y-direction polarized component of light that has
entered. In this manner, the polarizer 141 and the polarizer 143
may allow different polarized components of the light to pass
therethrough. For example, the polarization direction of the light
allowed to pass therethrough may differ by approximately 90.degree.
between the polarizer 141 and the polarizer 143, as in this
example.
[0123] The optical shutter operation signal S41 may be inputted
into the high-voltage power source 144 of the optical shutter 41.
When the optical shutter operation signal S41 is inputted to the
high-voltage power source 144, the high-voltage power source 144
may apply a voltage S61 to the Pockels cell 142. The voltage S61
may have a pulse duration (time length) that is essentially the
same as the pulse duration of the optical shutter operation signal
S41. The Pockels cell 142 can, for example, change the polarization
direction of inputted light during the period in which the voltage
S61 is being applied. In this example, the voltage S61 having a
voltage value that changes the polarization direction of the
inputted light by approximately 90.degree. may be applied to the
Pockels cell 142 from the high-voltage power source 144.
[0124] Pulsed laser light L0 that enters the optical shutter 41
from the long-pulse master oscillator 60 may first enter the
polarizer 141. The polarizer 141 may allow the Y-direction
linearly-polarized component of the inputted pulsed laser light L0
(called "Y linearly-polarized pulsed laser light" hereinafter) to
pass therethrough. The Y linearly-polarized pulsed laser light that
has passed through the polarizer 141 enters the Pockels cell
142.
[0125] In the case where the voltage S61 is not being applied to
the Pockels cell 142, the Y linearly-polarized pulsed laser light
that has entered the Pockels cell 142 can be outputted from the
Pockels cell 142 as-is, as Y-direction linearly-polarized light,
and can enter the polarizer 143. Accordingly, the Y
linearly-polarized pulsed laser light that has passed through the
Pockels cell 142 can be reflected and absorbed by the polarizer
143. As a result, the pulsed laser light L0 can be blocked by the
optical shutter 41.
[0126] On the other hand, in the case where the voltage S61 is
being applied to the Pockels cell 142, the polarization direction
of the Y linearly-polarized pulsed laser light that has entered the
Pockels cell 142 can be changed by approximately 90.degree.. As a
result, X-direction linearly-polarized pulsed laser light (called
"X linearly-polarized pulsed laser light" hereinafter) can be
outputted from the Pockels cell 142. This X linearly-polarized
pulsed laser light passes through the polarizer 143. As a result,
pulsed laser light L1 is outputted from the optical shutter 41.
[0127] In addition, assuming that, for example, the required pulse
duration (time length) for the pulsed laser light L1 is
approximately 20 ns, it is preferable, for example, for the voltage
S61 having a pulse duration (time length) of approximately 20 ns to
be applied to the Pockels cell 142, as shown in FIG. 15. Meanwhile,
as described above, pulsed laser light having, for example, a pulse
duration (time length) that is sufficiently greater than the jitter
of the rise timing may be outputted from the long-pulse master
oscillator 60. Assume, for example, that the jitter of the rise
timing is approximately .+-.10 ns, and that the required pulse
duration (time length) for the pulsed laser light L1 is
approximately 20 ns. In this case, as shown in FIG. 16, it is
preferable for the long-pulse master oscillator 60 to output, for
example, the pulsed laser light L0 having a pulse duration (time
length) of approximately 70 ns. Through this, as shown in FIG. 17,
the pulsed laser light L1 having a pulse duration of approximately
20 ns may be outputted from the optical shutter 41, at a timing
that is not affected by the jitter in the rise timing of the pulsed
laser light L0. Note that a typical Pockels cell has a
responsiveness of several ns, and thus is suitable in optical
shutters for laser systems in which high-speed switching is
demanded.
[0128] Note that the present example is a configuration in which
the polarization directions of the pulsed laser light L0 that has
passed through the polarizer 141 and the pulsed laser light L1 that
has passed through the polarizer 143 have been changed to differ
from each other by approximately 90.degree.. For this reason, the
optical shutter 41 is said to be in an open state during the period
in which the voltage S61 is applied to the Pockels cell 142.
However, the disclosure is not limited to this example. For
example, the polarization directions of the pulsed laser light L0
that has passed through the polarizer 141 and the pulsed laser
light L1 that has passed through the polarizer 143 may be the same
direction. In this case, the optical shutter 41 is said to be in an
open state during the period in which a voltage is not applied to
the Pockels cell 142. Note that an optical shutter being in an
"open state" refers to putting the optical shutter in a state in
which pulsed laser light can pass therethrough, whereas an optical
shutter being in a "closed state" refers to putting the optical
shutter in a state in which pulsed laser light is blocked
thereby.
5.2 Operations
[0129] Next, an overview of the operations performed by the laser
system 1B will be given. The overall operations of the laser system
1B may be similar to those of the laser system 1A shown in FIG. 2.
However, with the laser system 1B, the optical shutter operation
signal S41 may be inputted into the optical shutter 41 from the
controller 210. The optical shutter operation signal S41 may be
inputted into the optical shutter 41 via the shutter delay circuit
341. Through this, the optical shutter 41 may open/close so that
part of the pulsed laser light L0 outputted from the long-pulse
master oscillator 60 is cut out.
[0130] Other operations are the same as those of the laser system
1A shown in FIG. 2.
5.3 Effects
[0131] By employing the configuration and operations as described
above, in the third embodiment, the laser controller 220A may
detect a difference between the timing of the pulsed laser light L1
cut out by the optical shutter 41 (for example, the oscillation
timing Tmo) and the timing of a discharge (for example, the
discharge timing Tpo). In accordance with that difference, the
laser controller 220A may carry out feedback control on an
opening/closing timing Top of the optical shutter 41 and the
discharge timing Tpo of the amplification device 3A. Through this,
a discharge can be caused to occur in the discharge space 23 in
correspondence with the timing at which the pulsed laser light 32
passes through the discharge space 23 within the amplification
device 3A. As a result, the pulsed laser light 32 can be amplified
in a more stable manner without being influenced by drift in the
opening/closing timing Top and the discharge timing Tpo.
[0132] In addition, in the third embodiment, the pulsed laser light
L1 outputted from the optical shutter 41 may be caused to take on a
pulse shape cut out from the pulsed laser light L0 based on the
optical shutter operation signal S41 supplied to the optical
shutter 41. In this manner, the pulsed laser light L1 may be
controlled by the optical shutter operation signal S41 supplied to
the optical shutter 41. For this reason, it is thought that jitter
in the pulsed laser light L1 will become circuit jitter in the
high-voltage power source 144 that applies the voltage S61 to the
Pockels cell 142. It is furthermore thought that such circuit
jitter is sufficiently short relative to the jitter of the pulsed
laser light L0 outputted from the long-pulse master oscillator 60.
Therefore, it is thought that the jitter in the pulsed laser light
L1 that has passed through the optical shutter 41 is low enough to
be ignored.
[0133] The master oscillator 2B can control the pulse duration
using the optical shutter 41. Accordingly, it is also possible to
change the pulse duration with ease.
5.4 Flowchart
[0134] Next, operations performed by the laser system 1B
illustrated in FIG. 13 will be described in detail with reference
to the drawings. However, because the general operations of the
laser system 1B as a whole are the same as the operations
illustrated in FIG. 8, the descriptions of those operations will be
repeated here.
[0135] FIG. 18 illustrates an overview of the operations in the
parameter initializing routine indicated in step S101 of FIG. 8. As
shown in FIG. 18, in the parameter initializing routine according
to the third embodiment, the laser controller 220A may obtain the
oscillation delay time Ddp set in the oscillation delay circuit 311
(step S221). The obtained oscillation delay time Ddp may be a
default value stored in advance in a memory or the like (not
shown), or may be a value newly calculated by the laser controller
220A. Continuing on, the laser controller 220A may set the obtained
oscillation delay time Ddp in the oscillation delay circuit 311 via
the controller 210 (step S222). Through this, the timing of the
pumping laser oscillation signal S11 that passes through the
oscillation delay circuit 311 may be delayed by an amount
equivalent to the oscillation delay time Ddp.
[0136] Next, the laser controller 220A may obtain the shutter delay
time Dop set in the shutter delay circuit 341 (step S223). The
obtained shutter delay time Dop may be a default value stored in
advance in a memory or the like (not shown), or may be a value
newly calculated by the laser controller 220A. Next, the laser
controller 220A may set the obtained shutter delay time Dop in the
shutter delay circuit 341 via the controller 210 (step S224).
Through this, the timing of the optical shutter operation signal
S41 that passes through the shutter delay circuit 341 may be
delayed by an amount equivalent to the shutter delay time Dop.
[0137] Next, the laser controller 220A may obtain a time for which
to put the optical shutter 41 into the open state, or in other
words, a cutout time of the pulsed laser light L1 (an optical
shutter open time .DELTA.Top) (step S225). The obtained optical
shutter open time .DELTA.Top may be a default value stored in
advance in a memory or the like (not shown), or may be a value
newly calculated by the laser controller 220A.
[0138] Next, the laser controller 220A may obtain the switch delay
time Dpp set in the switch delay circuit 350 (step S226). The
obtained switch delay time Dpp may be a default value stored in
advance in a memory or the like (not shown), or may be a value
newly calculated by the laser controller 220A. Then, the laser
controller 220A may set the obtained switch delay time Dpp in the
switch delay circuit 350 (step S227). Through this, the timing of
the switch signal S5 that passes through the switch delay circuit
350 may be delayed by an amount equivalent to the switch delay time
Dpp.
[0139] Next, the laser controller 220A may obtain a time to turn
the switch 25 on, or in other words, a time for which to apply a
discharge voltage between the anode 21 and the cathode 22 (that is,
the switch-on time .DELTA.Tpp) (step S228). The obtained switch-on
time .DELTA.Tpp may be a default value stored in advance in a
memory or the like (not shown), or may be a value newly calculated
by the laser controller 220A. Thereafter, the laser controller 220A
may return to the operations indicated in FIG. 8.
[0140] Operations started by the controller 210 in step S103 of
FIG. 8 will now be described. As shown in FIG. 19, under the
control of the laser controller 220A, the controller 210 may stand
by until, for example, the trigger signal S1 is received from the
laser controller 220A (step S231; NO). Note that the controller 210
may transmit the internal trigger oscillated by the internal
trigger oscillator 211 at a predetermined repetition rate to the
pumping laser 5 as the pumping laser oscillation signal S11 during
the period in which the trigger signal S1 is not being inputted
from the laser controller 220A at an approximately predetermined
repetition rate.
[0141] When the trigger signal S1 has been received (step S231;
YES), the controller 210 may transmit the pumping laser oscillation
signal S11 to the pumping laser 5 (step S232). Furthermore, the
controller 210 may also start transmitting the optical shutter
operation signal S41 to the optical shutter 41 (step S233). The
pumping laser oscillation signal S11 may be inputted to the pumping
laser 5 through the oscillation delay circuit 311. The optical
shutter operation signal S41 may be inputted to the optical shutter
41 through the shutter delay circuit 341. The oscillation delay
circuit 311 may be set so as to delay the pumping laser oscillation
signal S11 by an amount equivalent to the oscillation delay time
Ddp. The shutter delay time Dop may be set in the shutter delay
circuit 341 so that the optical shutter 41 carries out
opening/closing operations in correspondence with the timing at
which the pulsed laser light passes therethrough. Through this, the
timing at which the pumping light 51 is outputted from the pumping
laser 5 and the timing at which the optical shutter 41 opens and
closes may be adjusted. Note that the timing at which the pumping
light 51 is outputted from the pumping laser 5 may be directly
related to the timing at which the pulsed laser light L0 is
outputted from the long-pulse master oscillator 60.
[0142] Thereafter, the controller 210 may measure the time that has
elapsed after the start of the transmission of the respective
optical shutter operation signal S41 using, for example, a timer or
the like (not shown). The controller 210 may then stand by until
this measured time has become greater than or equal to the pre-set
optical shutter open time .DELTA.Top (step S234; NO).
[0143] When the optical shutter open time .DELTA.Top has elapsed
(step S234; YES), the controller 210 may end the transmission of
the optical shutter operation signal S41 (step S235). Through this,
the optical shutter 41 may enter the closed state. Note that as
described above, using the long-pulse master oscillator 60 may make
it possible to adjust the waveform of the pulsed laser light L1,
using the opening/closing operations of the optical shutter 41.
[0144] Next, the controller 210 may stand by until the result of
detecting the pulsed laser light L1 is inputted from the optical
sensor 410 (step S236; NO). When the detection result is inputted
from the optical sensor 410 (step S236; YES), the controller 210
may transmit the inputted detection result to the laser controller
220A (step S237). After this, the controller 210 may determine
whether or not an end to the operations has been specified by the
laser controller 220A or the like (step S238). In the case where
the end has been specified (step S238; YES), the controller 210 may
end the present operations. However, in the case where the end has
not been specified (step S238; NO), the controller 210 may return
to step S231.
[0145] Next, operations started by the laser controller 220A in
step S104 of FIG. 8 will be described. As shown in FIG. 20, the
laser controller 220A may stand by until the trigger signal S1 is
outputted to the controller 210 at an approximately predetermined
repetition rate (step S241; NO). When the trigger signal S1 is
outputted (step S241; YES), the laser controller 220A may start the
transmission of the switch signal S5 to the switch 25 (step S242).
The switch signal S5 may be inputted to the switch 25 through the
switch delay circuit 350. The switch delay time Dpp may be set in
the switch delay circuit 350 so that a discharge occurs in the
discharge space 23 in correspondence with the timing at which the
pulsed laser light 32 passes through the discharge space 23.
[0146] Thereafter, the laser controller 220A may measure the time
that has elapsed after the start of the transmission of the switch
signal S5 using, for example, a timer or the like (not shown). The
laser controller 220A may then stand by until the measured time
becomes greater than or equal to the pre-set switch-on time
.DELTA.Tpp (step S243; NO).
[0147] When the switch-on time .DELTA.Tpp has elapsed (step S243;
YES), the laser controller 220A may end the transmission of the
switch signal S5 (step S244). Through this, the period in which a
discharge occurs in the discharge space 23 may be adjusted.
Thereafter, the laser controller 220A may determine whether or not
to end the operations (step S245). In the case where the operations
are to be ended (step S245; YES), the laser controller 220A may end
the present operations. However, in the case where the operations
are not to be ended (step S245; NO), the laser controller 220A may
return to step S241.
[0148] Next, step S108 of FIG. 8 will be described in detail. As
shown in FIG. 21, the laser controller 220A may specify the
opening/closing timing Top based on the result of the detection
performed by the optical sensor 410 that has been inputted from the
controller 210 (step S251). In addition, the laser controller 220A
may specify the discharge timing Tpo from the detection result
inputted from the sensor 430 (step S252).
[0149] Next, the laser controller 220A may calculate the delay time
D of the discharge timing Tpo relative to the opening/closing
timing Top (step S253). Next, the laser controller 220A may
calculate the error .DELTA.pp of the delay time D relative to the
delay time DO that has been set as a reference (step S254). The
laser controller 220A may then correct the switch delay time Dpp
(or the oscillation delay time Ddp and the shutter delay time Dop)
using the calculated error App (step S255). Thereafter, the laser
controller 220A may advance the process to step S109 of FIG. 8.
6. Additional Descriptions
[0150] Next, additional descriptions of the various portions
described in the aforementioned embodiments will be given.
6.1 Ti:Sapphire Laser
[0151] FIG. 22 illustrates an example of the aforementioned
Ti:sapphire laser 6. As shown in FIG. 22, the Ti:sapphire laser 6
may be what is known as a Littman-type laser. The Ti:sapphire laser
6 includes a high-reflection mirror 61, an output coupling mirror
65, a Ti:sapphire crystal 62, a grating 63, and a high-reflection
mirror 64. The high-reflection mirror 61 and the output coupling
mirror 65 form an optical resonator. The Ti:sapphire crystal 62 and
the grating 63 are disposed in the optical path of this optical
resonator. The high-reflection mirror 64 reflects laser light
diffracted by the grating 63 to return back toward the grating 63.
The high-reflection mirrors 61 and 64 form a resonator that is
separate from the resonator formed by the high-reflection mirror 61
and the output coupling mirror 65. The output coupling mirror 65,
meanwhile, also functions as an optical output terminal for
outputting the pulsed laser light L0.
[0152] The high-reflection mirror 61 allows the pumping light 51
from the pumping laser 5 to pass therethrough and reflects the
pulsed laser light from the Ti:sapphire crystal 62 thereby. The
pumping light 51 inputted via the high-reflection mirror 61 enters
the Ti:sapphire crystal 62. The optical input/output terminal
surfaces of the Ti:sapphire crystal 62 are cut to a Brewster's
angle. Through this, the reflection of laser light at these
terminal surfaces is suppressed. The Ti:sapphire crystal 62 which
the pumping light 51 has entered outputs the pulsed laser light L0
through oscillation using the energy obtained from the pumping
light 51 that travels back and forth within the resonator. The
pulsed laser light L0 emitted from the Ti:sapphire crystal 62 is
diffracted by the grating 63. Here, the output coupling mirror 65
is disposed relative to the grating 63 in, for example, the
emission direction of zero-order diffracted light. In addition, the
high-reflection mirror 64 is disposed relative to the grating 63 in
the emission direction of .+-.m-order diffracted light. According
to this configuration, by adjusting the angle of the
high-reflection mirror 64 relative to the grating 63, the
wavelength of the pulsed laser light L0 outputted by the
Ti:sapphire laser 6 can be selected. As a result, it is possible to
control the spectral linewidth of the pulsed laser light L0
outputted by the Ti:sapphire laser 6 to a spectral linewidth whose
chromatic aberration can be ignored at the time of exposure.
6.2 Amplifier (PA)
[0153] FIG. 23 is a diagram illustrating an example of the
aforementioned amplifier 7. Note that in this example, a multipass
amplification-type power amplifier that does not include an optical
resonator is given as an example. As shown in FIG. 23, the
amplifier 7 includes a plurality of high-reflection mirrors 72
through 78 and a Ti:sapphire crystal 71. The plurality of
high-reflection mirrors 72 through 78 forms multiple passes so that
the pulsed laser light L1 inputted from the Ti:sapphire laser 6
through the optical shutter 41 passes through the Ti:sapphire
crystal 71 a plurality of times (in the present example, four
times). The pumping light 51 from the pumping laser 5 enters the
Ti:sapphire crystal 71 through the high-reflection mirror 72. The
optical input/output terminal surfaces of the Ti:sapphire crystal
71 are cut to a Brewster's angle. The Ti:sapphire crystal 71
oscillates while obtaining energy from the pumping light 51 based
on the pulsed laser light L1 that advances through the multiple
passes. Through this, the pulsed laser light L1 undergoes multipass
amplification with each of the plurality of passes. As a result,
pulsed laser light L1a that has been amplified is emitted from the
amplifier 7. Note that the high-reflection mirror 72 allows the
pumping light 51 to pass but reflects the laser light from the
Ti:sapphire crystal 71.
6.3 Amplifier Including Optical Resonator (PO)
[0154] It is also possible to replace the amplifier 7 with a power
oscillator that includes an optical resonator therein. FIG. 24
illustrates the general configuration of a Fabry Perot-type
amplifier 7A. As shown in FIG. 24, the amplifier 7A includes a
high-reflection mirror 172, an output coupling mirror 173, a
Ti:sapphire crystal 174, and a high-reflection mirror 171. The
high-reflection mirror 172 and the output coupling mirror 173 form
an optical resonator. The Ti:sapphire crystal 174 is disposed in
the optical path in this optical resonator. The high-reflection
mirror 171 leads the pulsed laser light L1 inputted from the
Ti:sapphire laser 6 through the optical shutter 41 and the pumping
light 51 from the pumping laser 5 into the optical resonator.
[0155] The high-reflection mirror 171 reflects the pulsed laser
light L1 from the Ti:sapphire laser 6 toward the optical resonator,
and allows the pumping light 51 from the pumping laser 5 to pass
toward the optical resonator. In addition, the high-reflection
mirror 172 of the two that form the optical resonator allows the
pulsed laser light L1 and the pumping light 51 to pass and reflects
laser light from the Ti:sapphire crystal 174. The optical
input/output terminal surfaces of the Ti:sapphire crystal 174 are
cut to a Brewster's angle. Through this, the reflection of laser
light at these terminal surfaces is suppressed. By oscillating
while obtaining energy from the pumping light 51 based on the
pulsed laser light L1 that travels back and forth within the
optical resonator, the Ti:sapphire crystal 174 emits the amplified
pulsed laser light L1a. The pulsed laser light L1a that has been
amplified is outputted via the output coupling mirror 173.
[0156] The aforementioned descriptions are intended to be taken
only as examples, and are not to be seen as limiting in any way.
Accordingly, it will be clear to those skilled in the art that
variations on the embodiments of the present disclosure can be made
without departing from the scope of the appended claims.
[0157] The terms used in the present specification and in the
entirety of the scope of the appended claims are to be interpreted
as not being limiting. For example, wording such as "includes" or
"is included" should be interpreted as not being limited to the
item that is described as being included. Furthermore, "has" should
be interpreted as not being limited to the item that is described
as being had. Furthermore, the indefinite article "a" or "an" as
used in the present specification and the scope of the appended
claims should be interpreted as meaning "at least one" or "one or
more."
[0158] Although the aforementioned embodiment describes an example
in which there is one amplifier 7, a plurality of amplifiers 7 may
be used. Furthermore, although the Ti:sapphire laser 6 and the
amplifier 7 are pumped by a shared pumping laser 5, separate
pumping lasers may be used. In addition, a laser that oscillates
second harmonic light of an Nd:YLF laser or an Nd:YVO.sub.4 laser
may be used as the pumping laser 5. In addition, a laser that emits
second harmonic light of an erbium-doped fiber-optic laser may be
used in place of the Ti:sapphire laser 6. This laser may be pumped
using a semiconductor laser. Furthermore, the wavelength conversion
unit 8 is not limited to the configuration described in the present
disclosure, and any configuration may be employed as long as the
light entering the wavelength conversion unit 8 is converted into
light having a wavelength in the gain bandwidth of the
amplification device 3, such as, for example, a wavelength of
approximately 193 nm. For example, a CLBO crystal may be used
instead of the LBO crystal 9 as the wavelength conversion element
included in the wavelength conversion unit 8.
* * * * *